package com.justnow.offer;

import java.util.Scanner;

/**
 * @author justnow
 * Created on 2020-09-02
 * Description
 */
public class Solution1 {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        if (n <= 0 || n > 36) {
            System.out.println(0);
            return;
        }

        int[] dp = new int[n+1];
        dp[1] = 1;
        dp[2] = 2;
        for (int i = 3; i <= n; i++) {
            dp[i] = dp[i-1] + dp[i-2];
        }
        System.out.println(dp[n]);
    }
}
